1. Field of the Invention
The present invention relates to a method for producing a sintered magnet, more particularly, it relates to a method for producing the sintered magnet having excellent magnetic properties which is available to be produced in a high productivity.
2. Description of the Related Art
As a method for producing a sintered magnet, a dry forming method (for example, JP Patent Laid Open No. 2004-296849) and a wet forming method (for example, JP Patent No. 3833861) are known. In the dry forming method, a preform body is formed by pressure forming the dried magnetic powder and applying the magnetic field, then, firing the preform body. In the wet forming method, a liquid component is removed by pressure forming the slurry which includes the magnetic powder while applying a magnetic filed to form the preform body, then firing the preform body.
In the wet forming method, there is an advantageous point that required time for forming step is short since the dried powder is pressure formed in a mold, however it is difficult to improve the orientation ratio of the magnetic powder due to the magnetic field at the time of forming. As a result, the magnetic property of the obtained sintered magnet is lower than the sintered magnet obtained by the wet forming method. Further, in the wet forming method, the magnetic powder tends to be oriented easily by the magnetic field at the time of forming thus the magnetic property of the sintered magnet is excellent, however there is a problem that it takes a long time for forming, because the pressure is applied together with the removal of the liquid component.
Note that, as shown in JP Patent No. 3229435, it is proposed that a method for forming the kneaded pellet including the magnetic powder and the binder resin by injecting into the mold wherein the magnetic field is applied. However, by such method in which it is injection molded in a mold wherein the magnetic field is applied, when forming the kneaded pellet, the magnetic powder with a fine particle size tends to disperse non-uniformly due to the aggregation of the magnetic powder of the fine particle size particularly, there is a problem that the magnetic orientation of the magnetic powder cannot be made well in subsequent injection molding.
The present invention is made by considering these circumstances, and a purpose of the invention is to provide a method for producing the sintered magnet which is available to produce the sintered magnet with a high magnetic property with a high productivity.